Solar energy systems are of greatly increased interest due to rising energy demands worldwide and consequent rising prices for existing energy resources, especially petroleum resources. While much effort is being focused upon developing more efficient photovoltaic (PV) cells that can generate ever greater amounts of electrical energy based upon a given amount of solar radiation directed upon those cells, high efficiency PV cells nevertheless remain expensive. A less-expensive alternative to employing high efficiency PV cells is to employ low (or lower) efficiency PV cells. However, such PV cells need to be implemented across larger surface areas in order to collect sufficient solar radiation so as to generate the same amount of energy as can developed using high efficiency PV cells having a smaller surface area.
Although the efficiency of a PV-based solar energy system depends upon the efficiency of the PV cell(s) employed in that system, the amount of energy generated by such a system can also be enhanced without increasing the efficiency of the PV cell(s) or larger area PV cell(s) by combining the use of PV cell(s) with additional devices that concentrate the solar radiation prior to directing it upon the PV cell(s). Because such solar concentration devices can employ components that are less expensive than the PV cell(s) themselves, a solar energy system employing such a solar concentration device in combination with PV cell(s) covering a relatively small surface area can potentially produce, at a lower cost, the same high level of energy output as that achieved by a solar energy system employing only PV cell(s) of the same or greater area. Also, a solar energy system employing such a solar concentration device in addition to high efficiency PV cell(s) covering a relatively small area can achieve higher levels of energy output than would be possible using those PV cell(s) alone, even if those cells covered a large area.
While potentially providing such advantages, existing solar energy systems employing both PV cell(s) and solar concentration devices have certain disadvantages as well. In particular, some stationary solar concentration devices tend to be not very efficient. For example, one particular type of existing solar energy system employing both PV cell(s) and solar concentration devices is a system employing one or more fluorescent solar concentrators (FSCs). In such a device, light incident on the surface of a slab waveguide is absorbed by an atomic or molecular transition of material embedded in the slab. Upon absorption, some of the energy is then emitted as fluorescence uniformly in all directions, and this fluorescent light is emitted at a longer wavelength with less energy than the incident light. While a fraction of the emitted fluorescence is trapped within the slab, and guided to an edge of the waveguide for illumination of a PV cell, a large fraction of the fluorescent light is re-absorbed and re-emitted into a non-guided direction, thus resulting in substantial inefficiency.
An additional problem associated with some conventional solar concentrators (e.g., imaging lens or mirror-based concentrators) is that, for proper operation, such solar concentrators require sunlight that is incident from a particular direction relative to the concentrator. That is, while such solar concentrators are able to condense/magnify light incident over a large area onto a smaller area PV cell, such large magnifications require precise alignment that must be maintained as the sun moves through the sky through the daily arc, and through the seasonal variation of elevation. Although it is possible to achieve such alignment by way of an “active” system that uses tracking (with or without positional feedback, such active systems are expensive and often complicated to implement. The alternative, “passive” systems, which do not use active alignment, can achieve only a relatively small concentration factor (e.g., of approximately 10 suns), depending on the range of angles over which the concentrator is designed to maintain relatively high throughput efficiency.
Still another disadvantage associated with at least some conventional solar energy systems employing solar concentrators is that they are complicated and/or expensive to manufacture.
It would therefore be advantageous if an improved design for a solar energy system employing both PV cell(s) and solar concentration devices could be developed. More particularly, it would be advantageous if such an improved design allowed for one to achieve one or more of the benefits of conventional solar energy systems employing both PV cell(s) and solar concentration devices, while not suffering from (or suffering as much from) one or more of the above-described disadvantages of such systems.